Do not forget
Avoid heavy luggages : often, the hotels and buildings have no elevator. Shirts or T shirt are compulsory in the streets and you must be protected against sun.
If you forget your sun glasses, you will easily buy them at Lignano.
Bring also a beach towel (except if the hotel gives you one) because the sand can be very hot on the afternoon. Moskito repellant (but you can buy it "alla farmacia")
You can forget the hairdryer. First because, there is one in the room or in the appartment. Second, because the air is dry and so the hair dryer is not really usefull. Do not forget the UV lence (the days are sunny) and the flash (to shoot photographes when you stroll by the streets at night) Bathing suit with or without bra (in the North of Italy, there is no real concern).
If you wish to go to a free beach do not forget your umbrella and your tongs if you wish to put your feet on the sand.
If your hotel has a pool, the bathing cap can be compulsory. So, do not forget "la cuffia". If you rent an appartment, bring a frying pan (they always forget to put one) and if you are French have bowls (Italians use cups).
If you want to put a pizza in your oven, bring the oven : it misses in all the appartments (may be, for the benefit of the surrounding restaurants)
A sun screen for the car even it is AC equiped